Yeh - you can access it through COM, but it's gonna take a bit of work to get it. Firstly - you are gooing to need to be running your PHP on a windows box (since you want to access all thos lovely Powerpoint COM objects).
Secondly, you are definetly going to need all the powerpoint objects installed on your machine - which more or less means installing the latest version of Powerpoint on your server.
Lastly - you are going to need to have a lot of time deciphering which parts of the Powerpoint COM objects contain the information you are interested in. There is little (if any) documentation on any of this, and the last time I tried accessing some excel workbooks (not using PHP) it took an age to get hold of the right book, the correct cell range etc.
Anyhow - this will be a cool project if you get it going...